System for simulating aircraft turbojet engine operation



April 26, 1960 c. J. D'AMlco sysTEM FOR SIMULATING AIRCRAFT TURBO-JET ENGINE OPERATION Filed Nov. 23, 1954 NIF mq INVENTOR CARMINE I. DAMIIZD f humbug m Il. o o d Q2 n ATTORNEY BY u Aaircraft engine.

United States Patent O SYSTEM FOR SIMULATING AIRCRAFT TURBO- JET ENGINE GPERATION Carmine I. DAmico, Union City, NJ., assignor to Curtiss-Wright Corporation, a corporation of Delaware This invention relates to means for simulating the operation ofaircraft turbo-jet engines, and in particular to means for simulating the speed response of aturbo-jet lever may be indirectly connected to the fuel controlr 2,933,828 Patented Apr. l26, 14960 ice connected through a gear reducer and mechanical con- K nection 11 to a pair of potentiometers 12 and'13 so as system through an intermediate system that limits or schedules the supply of fuel to the jet engine at a safe rate, regardless of the rate of throttle advance. Thus, the throttle-controlled scheduling system determines maximum rates of acceleration and deceleration of the jet turbine according to the enginecharacteristics and temperature limits.

A principal object of the present invention therefore is to provide an improved and realistic simulating system suitable for the ground training of aircraft personnel, adapted to represent the r.p.m. response of an aircraft jet engine turbine to throttle control and other conditions.

The invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. l is a partly diagrammatic and schematic illustration of analog computing circuits for representing the starting system, throttle control and r.p.m. computation and indication of a simulated aircraft turbo-jet engine; and

Fig. 2 diagrammatically illustrates typical turbine speed characteristic acceleration and deceleration curves of a turbo-jet engine of the type herein simulated.

Referring to Fig. 1, which illustrates the various control circuits and servo systems for computing turbine r.p.m., the primary servo system responsive to various factors for computing turbine r.p.m. (N) is generally indicated at 1 and comprises a conventional summing amplifier 2 having an input network generally indicated at 3 adapted to be energized by various alternating current signal voltages of varying magnitude and sense for computing N. An A.C. summing amplifier of this type is well-known in the art, the algebraic sum or resultant of the input signals being amplified to produce the output voltage. This amplified output voltage energizes the control coil 4 of an A.C. two-phase motor 5, the other coil 6 of which is energized by an A.C. reference voltage e1. The motor 5 drives a two-phase feedback generator 7 also having a reference voltage winding 8 energized by the reference voltage e2 and a feedback winding 9 for generating feedback voltage for the amplifier input network as hereinafter described. The operation of this type of motor is well-known, the motor-speed and direction being according to the magnitude and phase relation respectively of the current in the control winding 4 with respect to the reference voltage e1; also the phase relation and magnitude of the feedback voltage depend respectively on the direction and speed of rotation of the to adjust the respective slider contacts 14 and 15 according to the instantaneous position of the servo motor.

The potentiometers 12 and 13, as in the case of the other potentiometers indicated in the drawing, are actu,- ally of the circular wound-card type but are shown in a plane development for simplifying the disclosure. practice, the slider 14 for example is operated by a shaft disposed centrally of the circular card so as to make continuous contact therewith throughout the range of the servo motor. Accordingly the voltage derived at the slider contact represents a function, depending on the potentiometer design, of the computed r.p.m. quantity. Where the potentiometer is energized by a variableV voltage representing another factor, the derived slider voltage'` then represents the product of the combined functions.

The card 12 is energized at its upper terminal by 'a constant A.C. voltage -E (phased as indicated with respect to the system reference voltage) and is grounded at its lower terminal so that the voltage derived at slider 14 represents turbine r.p.m. (N) for use in the computing system as hereinafter described. The various potentiometer energizing voltages throughout the system are A.C. voltages and are indicated as having instantaneous polarity with respect tothe system reference voltage. The card 13, which is particularly designed for the starting operation, is adapted to be energized near its lower terminal by aconstant A.C. voltage -1-E from the start switch presently described and is grounded above the voltage supply tap at a point representing idle r.p.m. (N1). The voltage derived at slider 15 is fed by conductor lead 16 to the amplifier input network at terminal 17 for starting purposes. The servo motor also positions a switch cam 18 and an r.p.m. indicator '19.

An earlier system for computing turbo-jet r.p.m. under varying flight and engine conditions is disclosed and claimed in a copending application S.N. 291,254 filed vJune 2, 1952 by Stern et al., now Patent No.- 2,798,308,

and assigned to the same assignee as the present invention.

Starting operation (c) The start switch generally indicated at 22 is in the off position, and

(d) The firing relay 23 is `cle-energized and in the off position.

For simulating ground starting the pilot presses the start button 24, thereby holding the start switch 22 at on position. This represents that the engine starter has been engaged and is cranking. Accordingly the switch 25 is moved from its grounded a contact to its b contact which is connected to a constant A.C. source +B. Accordingly, the N card 13 is now energized through lead 26 from this source for supplying the starting r.p.m. potential. The resulting derived voltage at slider 15 is fed by conductor lead 16 to the N amplifier input terminal sliders upward on the cards) at a rate dependent jointly l on the design of the card 13 and the servo feedback; control presently described, until the slider 15 of card.

13 reaches the grounded tap at 27. 'At this point the starting voltage is removed from-the N input network and other voltage signals representing idle r.p.m. operation have been applied to the network. A s the N servo l pickswup starting r.p.mlthe servooperated switch cam aereas f r and lead 36 to the throttle ,Servo system (Th) generally indicated at 37. This system comprises a vservo amplifier T38, the output of which energizes a two-phase servo motor 39 of the type previously described for operating the slider 40 ofthe throttle servo card 41. The upper 'terminal of this card is energized by a constant A.C. `voltage :l-E and the lower terminal is grounded soV that ,the derived voltage at Yslider 40 represents thel programmed fcont'rol of fuel supply to the engine. This voltage is used for several purposes including an answer voltage v011 "conductor'42 for the throttle servo amplifier 38, an input voltage, leads 42 and 43,'fo`r the idle fuel flow thyratron for controlling idle r.p.m. (N1) generally indicated at 4 4, andY (for normal operation) an input voltage for terfrom card 41 includes lead 46, air plug card 47 and its lslider 48, lead 49, the a contact of N, switch 56 (closed in normal operation) the a contact of the firing relay switch 51 and lead 52 which is connected to the respec- 'tive proportioning input resistance at terminal 45.

Referring again to the starting switch 22 which is being held on by the pilot, the start switch 53 at the .'on position completes aground circuit at its b contact .for the firing relay 23 by way of lead 54,cam'switch 55 (which is closed bythe switch cam 56 when the throttle lever 31 is advanced to idle r.p.m. position), lead 55', N cam switch 30 (which is closed at starting values of r.p.m.), lead 57, instructors fuel available switch 58 on its a contact and lead 59 to one terminal of the Yfiring relay 23, the other terminal of which is energized by a D. C. voltage as indicated. When the firing relay is operated to the firing position its switch 60 is closed on its a contact to provide for the tiring relay a holding circuit including the throttle lever switch 61 that is closed by the switch cam 62 at, and above, idle r.p.m. position, lead 63 and the a contact of the instructors fuel available switch 64. When the energizing circuit of the vlfiring relay 23 is locked in by the aforesaid holding circuit, the pilot can release the start button 24.

While the s'tart switch is still on and prior to energization of the firing relay, the start switch 65 engaging `its `b contact completes V(in addition to the normal feedback circuit that includes lead 66 for the voltage Efbm Yfrom the feedback generator to the N input network terminal 67) a parallel feedback circuit from junction 268, lead 69, start switch 65 and lead 70 to the N input network terminal 71. Thus, the generator feedback potential represented by two voltages EMD and'Efm) is fed to the N input network through parallel circuits, thereby decreasing the effective circuit resistance and increas- "ing the 4feedback effect during the starting period. Thus, a comparatively retarded or .sluggish operation of the N .servo duringv starting is provided for simulating Vthe'com- 'paratively slow acceleration'of the turbine rotor during cranking. This multiple feedback effect is retained during startingas'long'as thering relay is in 'the' off posiitionf An alternate circuit :for Efb) is completed by the :start switch 65 when off engaging its a contact, thereby completing a parallel feedback circuit from feedback Vgeperator leads 66 and 66', junction 72, the .b (ot) balance. This balance is ofcourse contact of firing relay switch 73, lead 74, the a contact of start switch 65 and lead 70 to the input network. This is effective during engine shutdown or windmilling When the start button is released and the firing relay s energized for firing, the second feedback circuit is cutout for permitting the r.p.m. servo to pick up speed in simulation of actual firing of the engine.

Idle fuel flow and idle r.p.m. operation In practice, with the throttle lever set at idle r.p.m. position, the turbine upon firing rapidly'comes up to its idle r.p.m. speed and maintains this speed until the throttle is advanced further. The idle r.p.m. is determined by an adjustment of fuel flow at a definite rate, such as 900 pounds per hour for example, referred to as idle fuel flow. For simulating idle r.p.m. (N1) operation a thyratron including its input network is generally indicated at 44. When the `thyratron lires according to Vwellfknown practice in response to a pre-determined increase in positive potential on its control grid, the thyra tron relay 21 is energized'tooperatea plurality of switches Yas hereinafter described. The signal voltages energizing the thyratron input network represent respectively, fuel ow (WI) at terminal 75, servo throttle (Th) Aposition at terminal 76, a constant voltage -E representing idle fuel ow at terminal 77, and the actual turbine r.p.m. (N) at terminal 78. For stable operation the oppositely phased voltages representing Th and N at the terminals 76 and 78 are equaland so balance each other. Accordingly, when the positive fuel voltage -l-Wf is less than the idle fuel flow voltage 'Ei, the thyratron does not lire and hence the relay 21 is in the de-energized or idle position. However when |Wf exceeds E1 the increased positive voltage causes the Ni ythyratron to fire, thereby energizing the relay 21 and moving the relay switches to the normal position. This is the usual operating condition of the turbine.

Referring specifically to the N, signal input circuits, the

voltage Wf comes from a fuel servo generally indicated at 80 which includes a servo amplifier 81 and a servo motor and associated mechanism M for operating the slider contacts 82 and 83 of the Wfcards 84 and 85 respectively. The input network of the servo amplifier 81 is energized by a so-called fuel increment voltage ,at lterminal 86 representing the difference between total fuelflow and idle fuel flow. A system for producing this increment voltage is disclosed in the aforesaid copending application S.N. 291,254 referring specifically to Fig. 2 transformer terminal 68a. Another input is the derived W; answer voltage at input terminal 87 from slider 82 of card 84, this card being energized by a voltage -I-E opposite in sense to the aforesaid increment voltage. Another signal is a constant voltage -Ei at terminal 88 representing the idle fuel flow value previously referred to. It will therefore be seen that the algebraic summation of these inputs represents Wf, the engine fuel ow. The aforesaid answer voltage at slider 82 is also 'applied by lead 89 to the N1 input terminal 75, constitut- -slider 40 and leads 42 and 43, and the N signal is applied at terminal' 78 lfrom the slider 14 of the N card 12 by way'of 'lead 90, junction 91 and lead92'. As above pointed out, the N1 thyratron 44 remains unfired in idle" position as long as the throttleleverV Y31' remains at'the idle r.p.mf position, by reason of the fact that for this condition Wf=W andlthe'Th and N `signals are instable upset immediately um adverts 2f f1.1@ there 1 f assenso Throttle control Assuming now that the pilot advances the throttle -to increase turbine r.p.m. for normal operation, the apparatus will be put in the following condition:

(a) The air plug control 20 is in the open position,

(b) The N1 thyratron relay is now energized in the normal position,

v (c) The start button is at off, and

(d) The tiring relay is energized at tiring position.

Under these conditions a voltage from the slider 40 of the Th servo card 41 is fed as previously described to the air plug card 47, Ni switch 50, firing relayv switch 51 to the N input terminal 45 for representing a positive throttle control Th signal. This voltage will be diminished by the AP card 47 if the air plug is not in the fully open position. An answer voltage of opposite sense from the N answer card 12 is now fed from lead 90, junction `91, lead 93, the a contact of N1 switch 94, the a contact of tiring relay switch 95 and lead 96 to the N input terminal 97. As the throttle lever is advanced to increase the derived voltage at the throttle slider 32, the throttle servo 37 tends to follow the throttle position. However, as the pilot may advance the throttle lever too rapidly for direct fuel supply to the turbine, the throttle servo follows the throttle movement at a predetermined maximum speed for scheduling the fuel supply soas to prevent overheating from too much fuel in the turbine combustion chamber. As previously indicated, thethrottle lever voltage is fed through the throttle control selector switch 35 to the throttle servo amplifier V38 where it is balanced by the oppositely phased answer voltage from card 41. The response characteristics of this servo and the gear reduction ratio are such that the servo increases the derived voltage at slider 40 at a predetermined maximum rate, not withstanding sudden movement of the throttle to the full advanced position.

In the actual aircraft here simulated, the throttle lever normally controls the throttle servo through electric control circuits. If such circuits should become disabled, it is desirable that the pilot have available a socalled throttle control override switch for direct control of the throttle servo. This override switch is normally centered and is operable by the pilot to run the throttle servo in one direction or the other depending on whether the override switch is held at its advance or retarded position. When this switch is released it automatically centers itself to deenergize the throttle servo. When the pilot wishes to switch the control over to the override switch, he irst throws a throttle control selector switch to a switch position. This enables the override switch directly to control the throttle servo.

For simulating purposes, the throttle control selector switch 35 normally engages its a contact for completing the throttle lever control circuit from the throttle lever card 33 to the Th servo for usual operation. Where the instructor fails the throttle lever control by throwing the throttle fail switch 105 to the fail position so that the override switch control is now required, the selector switch 35 is moved to its b contact at the switch position to cut in the override switch 100. This switch may now be moved in one direction or the other depending on whether the throttle control is to be advanced or retarded. If the switch 100 is moved to engage its a contact, i.e. to close (retard) the throttle, the input signal on the Th servo lead 36 is grounded so that the positive answer voltage from card 41 tends to run the Th servo toward the closed position. If the pilot wishes to advance the throttle control, the override switch 100v is moved to engage its b contact, thereby connecting the Th input lead V36 to a voltage source -E. This voltage tends to run the Th servo toward the open position as long as the pilot holds the override switch on open or until `the opposed voltages are balanced at the fully-open throttle position.

During the aforesaid override switch operation, it is desirable that the Th servo be locked against drifting when the override switch is not operating. Accordingly, a servo locking relay 102 is provided with a switch 103 for short-circuiting the control winding of the Th servo motor 39 when the override switch is in neutral position. In the energized position of thev locking relay the short-circuit is removed and in the de-energized position the switch 103 engages its b contact toshort the motor winding, thereby electrically locking it in position. The control of the locking relay is through the throttle control selector switch 104, this switch when on throttle lever control engaging its a contact to complete an energizing circuit to ground for the relay coil. This circuit includes the D.C. source Eme) connected to the relay coil 102, lead'98, selector switch 104 on its a contact, the Yinstructors throttle fail switch 105 (normally on its a contact), lead 106, throttle circuit breaker 107 and the instructors A.C. power available switch 108 normally on its a contact. It will be noted that when the instructor fails either the throttle lever control or the A.C. power by throwing the switches 105 or.108 to fail, the above ground circuit is broken and the relay 102 is cle-energized to lock the throttle servo. This can also be simulated by tripping the throttle circuit breaker 107. Accordingly, in normal operation on throttle lever control the locking relay 102 is maintained energized, i.e. in the unlocked position.

When the selector switch 104 is moved to its b contact for switc control, the locking relay is now connected in circuit with the override switch 109 which is movable between its a and b contacts which are jointly connected as indicated to the normally grounded lead 106 previously described. Hence, when the override switch 109 is moved to engage either its a or b contact to close or open the throttle the locking relay 102 is temporarily energized to unlock the Th servo, thereby permitting so-called jogging control of the Th servo by the pilot through the override switch. Failure of the switch control can also be simulated by opening the A.C. power switch 108 or tripping the circuit breaker 107, thereby deenergizing the locking relay and locking the Th servo in xed position. Y

Referring to Fig. 2 which graphically illustrates typical turbine r.p.m. response to full throttleadvance for maximum acceleration, and for full throttleA retardation to idle r.p.m. for characteristic deceleration, the N servo system is provided with multiple feedback circuits adapted to function in combination with the throttle servo for simulating the turbine r.p.m. characteristics.. The usual feedback signal Efbu) at terminal 67 has previously been described in connection with the parallel feedback signal Efb) at terminal 71 for simulating starting characteristics. The feedback signal Efb) is not used after starting and while the engine is tired. For simulating normal acceleration and deceleration of the turbine a third feedback circuit in parallel with the first feedback circuit is connected to the N input terminal 110. This General operation Assuming now that the pilot has started the turbojet engine as previously described and that the engine is nowV fired and running at-idle r.p.m., the N servo is Venergized so as to run the servo to the position representing idle r.p.m. The input signals for this 'operation gcomprise -the normalfeedback signal Btw), a ground signaltroni-N, switch 50'at Vterminal 45, and a-Wf` signal from the W'; card'SS fat terminal 97." The secondand third feedback circuits are grounded. T he Mf'fuel signal is phased to run the N servo with minimum feedback effecttoward increased r.p.m. until the Wf servo reaches ythe idle fuel flow value indicated atV the ground tap 85 on card 85. The Wf servov continues to be adjusted tofward idle fuel flow and the N servo follows with diminishing speed'until there is a ground signal at Wf slider 83. At this point the N servo is de-energized at the'idle r.p.m. position as there are no energizing input signals for the N amplifier network. Since the operation ofthe N servo during idle r.p.m. depends ron the fuel ii'ow Wt'. signal, it will be apparent that retarding of the Vthrottle to a point indicative of less than the idle r.p.m. yalue is ineiiective'further to decrease r.p.m. below the idle value. N-Wlen the jet engine is operated in idle the fuel flow is kept Yconstant .at approximately 900 lbs. per hour. This isacc'omplis'lied by making the Changes 'in jet engine vr.p.m. compensate for 'simulated changes in fuel flow due to -variation's'irisimulated altitude and ram pressure as disclosed in .the aforesaid application S.N. 291,254. The ground vtap 85 on W1 card 85 represents a position of the W, servo for this value. fuel flour is varied due to a change in simulated altitude or ram pressure, the derived voltage from Wf card 85 applied to terminal 97 of the N servo causes this servo to run ina direction that will in turn cause the Wf servo to return to its idle fuel flow position. Under idle conditions the throttle has no control over the fuel ow or enginerpm.r

Assuming now that `the throttle is advanced beyond idle, the N, thyratron will tire and energize the relay 21 to the normal position. This is due to the increased +Th signal. The engine is now in its normal operating condition wherein it is tired and running above idle r.p.m. For this condition the input signals for the N servo now comprise a throttle signal Th(AP) (as modified by air plug opening) from the AP card 47 at input terminal 45, and an oppositely phased answer voltage from the N card 12 at input terminal 97. Accordingly for normal operation the N servo seeks to match the position of the throttle servo, the control nowhaving been transferred from fuel ow to throttle position. An additionalY feedback signal'Efb) is now applied tothe input terminal 110 for additional retarding 'of N acceler ation as previously described.

When the throttle lever in a jet airplane is advanced suddenly, the r.p.m. of the jet engine responds 1n a characteristic manner due to the inertia of the engine rotor and the programming of the engine control. This response to a throttle burst is here simulated as previously described by interposing a throttle servo between the throttle lever andthe N servo system. When the throttle lever is advanced suddenly, as for example from idle to take-off position, the throttle servo tends to follow-up but is limited by the maximum speed of the servo motor and the gear ratio between the motor and the potentiometer cards. This changes the virtually step input from the pilots throttle lever card to a steadily increasing voltage from the throttle servo card 41 until the new Th value is reached for stabilizing the N servo. The `gear ratio of the throttle servo and the velocity feedback system ofthe N servo above described are adjusted to achieve they desired r.p.m response to throttle burst as diagrammatic'ally illustrated by the'acceleration curve of v Fig. 2.

It will now be assumed that the airplane while in flight runs out of .fuel forexample, so that the engine is not'lired.V -This`is simulated by the instructor throwing the .fue'P switches 64 and 58 to the no fuel position thereby de-energizing the holding circuit of the ring relay 25; fCuttiug oithe fuel resultsy Lin a zeroW;

If,'under idle conditions the signal so that the N1 thyratron cuts out and the relay 21 returns to idle As the fuel switch 58 is also open the firing relay now cannot be energized by the pilots'start button 24. This represents a condition wherein the roto is windmilling under influence of the true airspeed (VT) of the airplane. The N servo input signals now include the feedback voltages from parallel connected feedback circuits Efbu) and BMZ) at terminals 67 and 71 for material feedback effect respectively, an airspeed voltage VT(AP) at terminal 45 and an answer r.p.m. voltage N at terminal 97 from the N servo card 12. The aforesaid airspeed voltage is suitably obtained from a VT computing system generally indicated at disclosed by way of example in a copending application S. N. 291,253, tiled June 2, 1952, by Stern et al. now Patent No. 2,784,501, and assigned to the same assignee as the present invention. The VT system includes an amplitier 116 the output of which energizes a transformer 117 for producing at terminals 118 a voltage -l-VT. This voltage energizes through lead 119 the air plug (AP) card 120 so that the voltage derived at slider 121 repre'- sents the airspeed voltage modified according to simulated opening of the air plug. This voltage is fed by lead 122 to the b contact of firing relay switch 51 and hence by lead 52 to the proportioning resistance of the N servo input at terminal 45. Accordingly, the tiring relay is effective to transfer control of the N servo from the throttle servo to airspeed control when the tiring relay represents an unlired condition of the turbine, thereby to simulate windmilling of the turbine rotor. This windmilling signal can be removed simply by closing the air plug lever 20 so that a VT-(AP) ground signal is obtained from the AP card 120, thereby enabling the remaining N answer voltage at input terminal 97 to run the N servo down to zero r.p.m.

The operation of the N servo system during simulated acceleration and deceleration of the turbine depends primarily on the N, system above described. When the yturbine is running on idle r.p.m. and fired, the N1 thyratron relay 21 is deenergized at idle position. That is, the N1 inputs are balanced to the extent that Wf--Ei and Th=N so that the resultant voltage is not suiciently positive to iire the thyratron. In this condition the N servo is on Wi control without reference to the precise throttle position below idle r.p.m. Thus, the N servo remains at the idle r.p.m. position as long as the throttle is not advanced beyond idle and the W, signal from the Wf card 85 does not exceed that representing idle fuel ow, i.e. a ground signal at tap 85'.

Assuming now that the pilot rapidly advances the throttle to accelerate the turbine, the N1 thyratron vis tired by reason of the predominating Th positive voltage over the more slowly responding N negative voltage. The thryratron relay is now on normal so .that the N servo control is transferred from fuel control to turbine r.p.m. control by the N1 switch 94. In accordance with the advanced throttle position and the resulting increased r.p.m., the Wf computed value also increases as disclosed in the aforesaid application S.N. 291,254 so that -l-Wf now exceeds El. Under these conditions, the N1 thyratron remains fired. If the throttle has been advanced to the fully open position the N servo followsup with a speed response characteristic indicated by the acceleration curve of Fig. 2.

It will now be assumed that the pilot rapidly retards the throttle to some intermediate position in advance of the idle position. In such a case the positive Th signal is less Vthan the slower responding negative N signal. However, the computed Wf positive signal is suf c'iently greater than the idle fuel flow negative signal -Ei that'the thyratron remains fired. [.s the positive V-lWf signal decreases for the adjustment to reduced r.p.m., the negative -N signal also decreases so that a stable condition vis reached wherein the Th and N 4signals 'aosasas balance each other. During this transient condition the thyratron remains fired. However, when the throttle is retarded to or below the idle position the resulting decrease in the |W signal now results in a negative signal predominating at theNi input so that the thyratron cuts out and the relay 21 returns to idle'position where r.p.m. control is transferred back to fuel iiow. Where the throttle is rapidly retarded from fully open to the idle position, the deceleration of the N servo follows the characteristic deceleration curve of Fig. 2.

For simulating trouble conditions an instructors potentiometer 125 is provided for introducing a trouble signal to the-N input terminal 126. The card is energized at its terminals by oppositely phased voltages and has a grounded center tap so that the adjustment of slider 127 by the instructors control dial 128 is effective to apply signals representing either increased or decreased r.p.m. to the N servo by lead 129, thereby to represent faulty operation of the turbine, such as bearing seize, damage by over-heating or over-speeding, etc.

It should be understood that this invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. Apparatus for simulating the speed response of a turbo-jet aircraft engine, comprising a simulated throttle, a first electrical servo system responsive to simulated throttle operation by the pilot for producing an electrical control quantity variable in magnitude, said throttle responsive servo lagging said throttle movement and having a predetermined maximum rate of speed so that said control quantity represents scheduled fuel supply to the engine independently of instantaneous throttle position, a second electrical servo system normally responsive to said electrical quantity and operable to represent turbine r.p.m., said second system including a plurality, of feedback proportioning resistances arranged to be selectively connected in the input of said second system according to different simulated engine operating conditions affecting the speed of the engine for receiving feedback signals, whereby the speed response of said second system is varied in response jointly to said electrical quantity and feedback signals for simulating the dynamic response characteristics of said engine.

2. Apparatus for simulating the speed response of a turbo-jet aircraft engine, comprising a simulated throttle, a first electrical servo system responsive to simulated throttle operation by the pilot for producing an electrical control quantity variable in magnitude at a predetermined maximum rate to represent scheduled fuel supply to the engine, a second electrical servo system normally responsive to said electrical quantity and operable to represent turbine r.p.m., said second system including feedback control means responsive to simulated engine operating conditions for varying the feedback characteristics, a third electrical system operable to produce an electrical quantity representing computed engine fuel iiow, means responsive jointly to all three electrical systems for representing idle fuel ow of the engine, and means including transfer circuit means adapted selectively to transfer control of the r.p.m. system from the throttle quantity to said fuel quantity in response to a simulated idle fuel ow condition, said transfer means also being operable to control said feedback means, whereby the speed response of said second system simulates the response characteristics of said engine. Y

3. Apparatus as specified in claim 2 wherein Ysaid transfer means is jointly responsive to electrical quantities representing respectively computed fuel ow, idle fuel iiow, throttle position and turbine r.p.m. for :selecting the transfer circuits according to simulated norma or idle engine condition.

4. Apparatus as specified in claim 2 including-means for producing an electrical quantity representing air speed of the aircraft, and relay means alternatively controlled according to simulated tired and un-fired conditions of theturbine for applying respectively the represented fuel quantity or air speed quantity to control the r.p.m. system for 'a fired or unfired condition, said relay means also being operable to control said feedback means whereby the response of said r.p.m. system simulates windmilling v of the turbine when the engine is un-fired.

5. Apparatus for simulating the speed response of a turbo-jet aircraft engine comprising an electrical servo system operable to represent a function of turbine r.p.m., a plurality of feedback circuits having different characteristics adapted to be connected to said servo system for varying the characteristic speed response thereof, start" control means operable by the pilot, means controlled by said start means for connecting at least one of said feedback circuits to the servo system for simulating the characteristic start response of the engine, and means controlled jointly by said start means and r.p.m. system for supplying potential to said r.p.m. system for operating said r.p.m. system to a position representing idle r.p.m., and for removing said potential at said position.

6. Apparatus for simulating the speed response of a turbo-jet aircraft engine, comprising a simulated throttle, a first electrical servo system responsive to simulated throttle operation by the pilot for producing an electrical control quantity variable in magnitude at a predetermined maximum rate to represent scheduled fuel supply to the engine, a second electrical servo system normally responsive to said electrical quantity and operable to represent turbine r.p.m., said second system including feedback control means responsive to different simulated engine operating conditions for varying the feedback characteristics, and means representing variable air plug opening for modifying the throttle electrical quantity that controls said second system, whereby the speed response of said second system simulates the response characteristics of said engine.

7. Apparatus for simulating the speed response of a turbo-jet aircraft engine, comprising a simulated throttle, a first electrical servo system normally responsive to simulated throttle operation by the pilot for producing an electrical control quantity variable in magnitude at a predetermined maximum rate to represent scheduled fuel supply to the engine, a second electrical servo system normally responsive to said electrical quantity and operable to represent turbine r.p.m., said second system including a feedback control means responsive to different simulated operating conditions for varying the feedback characteristics, control means for said first electrical system comprising a simulated throttle over-ride control and a simulated throttle control selector for transferring control of said first system from the throttle to the throttle over-ride, and vice versa, whereby the speed response of said second system simulates the response characteristics of said engine.

8. Apparatus as specified in claim 7 including means for locking said system in position to prevent drifting of throttle position and means controlled jointly by the throttler selector and throttle override for controlling the condition of said locking means.

9. Apparatus for simulating the speed response of a turbo-jet aircraft engine, comprising a simulated throttle, a first electrical servo system responsive to simulated throttle operation by the pilot for producing an electrical control quantity variable in magnitude at a predetermined maximum rate to represent scheduled fuel supply to the engine, a second electrical servo systemy normally responsive to said electrical quantity and operable to represent turbine r.p.m., said second system including feedback control means responsve to different simulated engine operating conditions for varying the feedback characteristics, said feedback means including a plurality of feedback vcircuits adapted to be connected in parallel to said sec- Qnd system, one of said circuits being connected@ said rid system v'for Yall conditions of," operation, s tat" means for initially energizing said second system and for connecting another circuit of said second system for added feedbackr effect during the engine starting, and transf/er means for controlling the energization of said second system after starting according to simulated normal or firdle, operation, said transfer means also adapted to c011-Y nect another feedback circuit to said system for simulating speed response during normal operation, whereby theV speed response of saidV second system simulatesy the respouse characteristics of said engine.

Y f Beweise-Cited in fhl'e 61e Qf this patent Iulrel'bachA etal. May 9, 1.950 Germanton .v Aug. 14, 1951 Kennedy Aug. 26, 1952 Wolin et al. Nov. 20, 195,6; Stern et al July 9, 1957 Stern et al. Oct. 8, 1957 

